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TC1796
Peripheral Units (Vol. 2 of 2)
Micro Second Channel (MSC)
User’s Manual
21-26
V2.0, 2007-07
MSC, V2.0
The content of bit field USR.URR determines the operation of an internal sampling
reload counter that is clocked with
f
MSC
.
shows the operation of the
sampling counter at the beginning of an upstream frame with a divide factor DF of 8
(OCSR.URR = 010
B
is equal to DF = 8) which means eight sampling clocks per each
frame bit cell.
When the upstream channel is in idle state it waits for a falling edge (1-to-0 transition) at
SI. Therefore, the sample counter starts counting up and is reset when the selected
divide factor DF shown in
is reached. In the middle of the sampling counter’s
count range, the logic state at SI is evaluated and, in case of a data bit, latched in the
receive buffer’s shift register. With the reload of the sampling counter, the shift register
is shifted by one bit position.
Figure 21-18 Upstream Channel Sampling with URR = 010
B
21.1.3.5 Spike Filter
The upstream channel input line SDI is sampled using a built-in spike filter with
synchronization stage, both clocked with
f
MSC
. The spike filter is a chain of flip-flops with
a majority decision logic (2 out of 3). A sampled value that is found at least twice in three
samples is taken as data input value for SI.
1
MCT05812_mod
Start Bit
SI
Reception
Enabled
f
BR
Sampling
Counter
D0
Sampling
Shifting
0
2 3
5
4
6 7
f
MSC
1
0
2 3
5
4
6 7
D1
2
0 1